Bacteriophage SP01 is chosen as a model system for development. Coordinate in vivo studies and in vitro studies of RNA and DNA-dependent protein synthesis will be directed at understanding how blocks of genes are regulated in transcription. A biochemical-genetic approach will be used, in which viral mutants will be employed to determine gene functions. Specific mechanisms under study will be modification of host RNA polymerase and the positive control mechanism determining initiation at new viral promotors. A program will be initiated to explore the role of proteolysis in viral head morphogenesis.